The invention pertains to plastic piping. More particularly, the invention pertains to secondary containment piping systems.
Secondary containment systems are either required by law or installed by end users to protect against accidental discharge of hazardous chemicals into the environment or to protect against personal injury. Secondary containment comprises an outer or containment pipe that surrounds the inner or primary fluid carrying pipe. Secondary containment systems can be either buried or above ground, pressure or drainage, and usually have some type of detection scheme to detect for any leaks. The most common systems in use today are joined by solvent cement with a much smaller percentage joined by heat fusion (for polyolefin materials). Most systems are sold with a standard pressure rating on the inner pipe and limited pressure rating for outside pipe (0.3 Bar is common). A common legal requirement is for these systems to contain a leaking fluid for up to seventy-two hours until a repair can be made.
An exemplary solvent cement containment piping system is made by utilizing existing molded pipe fittings; inserting a smaller inner fitting (tee, elbow etc.) within a larger outer fitting and providing a “centralizer” to support the two. Similarly, secondary containment pipes are made by inserting a smaller inner/main pipe within a larger outer/containment pipe and providing centralizers for support. Joining the pipes to the fittings has always been the most difficult task. Existing systems require a considerable number of simultaneous solvent-cemented joints for a typical installation. Typical solvent cementing requires: the application of a primer to both mating surfaces; then application of the cement to both surfaces (most times two applications of cement to the fitting side); then quickly joining the mating parts (applying a quarter turn in the process); and then holding the parts in place (thirty seconds to a minute) until the cement sets up.
Understandably, this process is even more difficult to accomplish when attempting to do an inner and outer joint at the same time. There are twice the number of surfaces that must be prepared, the inner pipe needs to be fixed to the containment pipe to ensure complete socket insertion. Also, the inner joint is being done “blind”. Other deficits of existing systems are inability to inspect the inner joint during pressure testing and, should a leak occur, difficulty locating and repairing a failed joint.
Existing systems provide “closure couplings” that are intended to be used at each of the final pipe segment joints. Exemplary closure couplings have two special coupling halves (with no internal pipe stops) which have a tapered male/female interface. One coupling half seals the outside of the containment pipe and the mating side is intended to slide over the gap area and seal the other pipe and the male/female interface of the coupling.